Don Lincoln on Particle Physics, Antimatter, and the Biggest Mysteries in Physics

Don Lincoln, a particle physicist at Fermilab with decades at the experimental frontier, covers the entire arc from Newton’s unification of gravity to the unsolved mysteries of antimatter asymmetry, dark matter, and dark energy — and explains why a theory of everything is probably centuries away.

Key ideas

1. Physics advances by unification. From Newton merging terrestrial and celestial gravity, to Maxwell unifying electricity and magnetism, to Weinberg, Glashow, and Salam merging electromagnetism and the weak force into the electroweak force: the history of physics is a sequence of recognising that apparently separate phenomena are facets of a single underlying principle.

2. The Higgs field is a Band-Aid on electroweak theory. Electroweak unification works at high energies where all force-carrying particles are massless. The Higgs field, which permeates all space and switched on at 10⁻¹² seconds after the Big Bang, breaks that symmetry at low energies — giving mass to the W and Z bosons while leaving the photon massless. The Higgs boson is the detectable ripple in that field; its discovery at CERN on 4 July 2012 closed 50 years of searching.

3. A theory of everything is not near. The energy scale at which all forces unify is roughly a quadrillion times higher than the most powerful accelerator we can build. Lincoln compares our position to Australopithecus in Africa trying to predict the Alps, penguins, and the Indian Ocean: local extrapolation fails at extreme distances. Superstring theory may be internally consistent but has not produced a single testable prediction after 50 years of effort.

4. Antimatter exists, but not enough of it. Matter and antimatter should have been created in equal quantities after the Big Bang. We see only matter. The observed excess implies a tiny asymmetry — one extra matter particle per billion matter-antimatter pairs — whose mechanism is unknown. Fermilab’s neutrino programme is searching for a difference in oscillation rate between neutrinos and antineutrinos (leptogenesis) as a possible explanation.

5. Dark matter is probably real; dark energy is the worst prediction in physics. The Bullet Cluster and the Dragonfly galaxies (DF-2, DF-4) provide strong evidence that dark matter is a genuine substance, not a correction to gravity. Yet its identity is entirely unknown despite three decades of searches. Dark energy — the repulsive force accelerating the universe’s expansion — is real by observation, but quantum field theory’s prediction for its magnitude is 10¹²⁰ times too large, making it the largest quantitative discrepancy in all of science.

Content

The long project of unification

Lincoln frames the history of physics as a succession of recognitions that apparently distinct phenomena are one and the same. Newton showed that the moon falls for the same reason your sandwich falls — terrestrial and celestial gravity are one force. Maxwell showed that a lightning bolt and a refrigerator magnet are governed by the same equations. Each step was counterintuitive at the time and obvious in retrospect.

The twentieth century pushed the project inside the atom. By the 1930s, physicists knew of four forces: gravity, electromagnetism, the strong nuclear force (which holds nuclei together), and the weak nuclear force (responsible for certain forms of radioactivity). In 1967, Weinberg, Glashow, and Salam showed that electromagnetism and the weak force are a single electroweak force at high energies. The apparent difference at everyday energies — the photon travels at the speed of light across the universe; the W and Z bosons barely reach across a proton — is explained by the Higgs mechanism.

How particle accelerators work

The key insight comes from Einstein’s E = mc²: energy and mass are interchangeable. Smash two particles together with enough energy in a small enough volume and that energy can materialise as new, heavier particles. Every particle you create must be paired with its antimatter counterpart — this is not a convention but a constraint of the laws of nature.

At Fermilab’s Tevatron, Lincoln’s team collided protons against antiprotons at near light speed. Their 1995 discovery of the top quark — the heaviest known particle — required six months of data to accumulate 38 candidates. At CERN’s Large Hadron Collider today, the same particle is produced at roughly one per second. The CMS detector (Lincoln’s experiment) is 70 feet long, five storeys tall, and weighs 14,000 tonnes; it takes 40 million snapshots per second and reduces them to 1,000 recorded events through a fast trigger system. Of those, graduate students pick out the handful that might be the next Nobel Prize.

The Higgs boson discovery

The Higgs boson was predicted in 1964, became theoretically necessary in 1967, and took until July 4th, 2012 to find. Lincoln describes wearing two hats in the run-up: competing to discover it at Fermilab while knowing that the LHC, with 10 times the collisions per second and 3.5 times the energy, was all but certain to get there first. Fermilab had narrowed the Higgs mass to a remaining window; the LHC announced the discovery two days later.

What the July 2012 announcement really established was a particle consistent with the Higgs — not definitive confirmation. Supersymmetry, then dominant, predicted five Higgs bosons, not one. Only over the subsequent 14 years of measuring the particle’s mass, spin (zero), and decay modes has the original 1964 theory been validated. The Higgs is not the most revolutionary discovery in physics — Lincoln places it below Einstein’s contributions — but it was the last missing piece of the Standard Model, closing 50 years of searching.

The nickname ‘God particle’ came from Leon Lederman’s publisher, not Lederman himself. His intended name was ‘the goddamn particle’, for how difficult it had been to find.

Theory of everything: the practical obstacle

String theory has not made a single falsifiable prediction in 50 years. Lincoln’s objection is not that it is wrong but that it is untestable: the energy scale at which stringy effects should appear is 10¹⁵ times beyond what any conceivable accelerator can reach. At current rates of improvement — roughly a factor of seven in energy per 20 years, a pace that itself cannot continue — the gap closes in something like 500 years, and that assumes no new physics intervenes.

His Australopithecus analogy is pointed. A hominid wandering a 10-metre patch of Africa can make accurate predictions for 100 metres. At 500 miles, he would never predict the Indian Ocean, sperm whales, or Antarctica. At 10 miles up, he would freeze and die. Extrapolating our present physics a quadrillion times in energy and expecting to get the right theory is precisely that kind of projection.

Lincoln’s alternative — which he calls ‘practical progress’ — is to look at things that disagree right now: the identity of dark matter, the mechanism of baryogenesis, the nature of space and time, anomalies in precision measurements. These are tractable. Dark matter’s discovery, for instance, would be a clue powerful enough to reshape the theoretical landscape.

Loop quantum gravity earns more credit than string theory: it is better developed, makes testable predictions (originally that the speed of light would depend on frequency — a prediction since revised when observations ruled it out), and is honest about its scope — it is a theory of quantum gravity, not a theory of everything.

Antimatter: the mystery of the missing half

Paul Dirac predicted the positron (antimatter electron) in 1928 when his attempt to merge quantum mechanics and relativity produced an equation with two solutions: one for the electron, one for something else. Carl Anderson discovered the positron in 1932. CERN has since constructed antimatter hydrogen atoms, cooled them to near absolute zero, and compared their spectral lines to ordinary hydrogen — they match. In 2023, the ALPHA experiment watched antimatter hydrogen fall under gravity and confirmed it falls downward, consistent with ordinary matter (to current precision).

The mystery is not antimatter’s existence — we make it routinely — but its absence from the observable universe. After the Big Bang, equal quantities of matter and antimatter should have existed. They should have annihilated. What we see instead — everything — implies a surplus of one matter particle per billion. The mechanism that produced this asymmetry (baryogenesis or leptogenesis) is unknown. Fermilab’s DUNE experiment will compare the oscillation rates of neutrinos and antineutrinos; a difference would be a significant clue. Production costs are also staggering: it took Fermilab about 25 billion years of running to produce one gram’s worth of antiprotons at its operational rate.

Dark energy: the worst prediction in physics

In 1998, astronomers measuring the expansion rate of the universe expected to see it decelerating — gravity from all that matter should slow it down. Instead, the expansion is accelerating. The repulsive force responsible is called dark energy, and it is probably a property of space itself (Einstein’s cosmological constant, which he added and then rescinded, now reinstated).

The problem: quantum field theory predicts the energy density of empty space by summing contributions from all quantum fields at all wavelengths. The result is 10¹²⁰ times larger than what astronomers measure. This is the largest quantitative disagreement between theory and observation in all of science. Even if some new physics cuts the calculation short at the energies we can reach with the LHC — reducing the mismatch by a factor of 10⁶⁰ — the number is still absurdly large. Something is deeply wrong in how the theories are being connected.

Dark matter: real but unknown

Lincoln was agnostic about dark matter 25 years ago — modified gravity or modified inertia seemed equally plausible. Two observations changed his mind. The Bullet Cluster: two galaxy clusters that passed through each other. The gas clouds (most of the ordinary mass) slammed together and stopped. The gravitational distortions (detectable via lensing) followed the galaxies — not the gas. That behaviour is exactly what dark matter predicts and cannot be explained by modified gravity. The Dragonfly galaxies (DF-2, DF-4): galaxies that rotate exactly according to Newton’s laws, with no apparent dark matter. A galaxy where dark matter is absent is, paradoxically, strong evidence that dark matter can be removed — that it is a genuine substance, not a fiction invented to patch the equations.

Dark matter is five times more abundant than ordinary matter. Its identity is unknown despite three decades of searches: underground detectors looking for a ‘wind’ of dark matter particles through the Earth; collider experiments looking for missing momentum when a dark matter particle escapes; telescopes searching for gamma rays from dark matter annihilation. None has found anything. The viable mass range extends from asteroid-scale to sub-electron — an enormous parameter space — and only small patches have been ruled out.

Fermilab, science communication, and the next generation

Lincoln grew up poor, without academically connected parents, in a small town. He was drawn to physics by science-fiction reading and the popular-science writing of Isaac Asimov, Carl Sagan, and George Gamow. He became a particle physicist over cosmology in the mid-1980s because particle physics let him measure things rather than speculate. He worked eight AM to midnight six days a week as a graduate student, voluntarily, because he could not imagine anything else he wanted to do.

His science communication — books, YouTube videos, public lectures — is aimed at replicating that access for the kid in Iowa or Montana who does not have educated parents to point the way. He knows it has worked: interns at Fermilab have told him they came because of a video or a book.

Related

• Lisa Randall on Dark Matter, Physics, and Extinction — overlapping territory: dark matter, the LHC, the Standard Model
• Lisa Randall — theoretical physicist; shares Lincoln’s focus on dark matter and the Higgs
• Sean Carroll on General Relativity, Quantum Mechanics, Black Holes and Aliens — complementary treatment of gravity, quantum mechanics, and the nature of space
• Lex Fridman — host